Dynamic Handgrip Research Articles

Muscle Blood Flow Responses to Dynamic Handgrip Exercise in Young Obese Adults

INTRODUCTION: Exercise intolerance is a hallmark characteristic of obesity, which may be related to an impaired ability to appropriately increase blood flow to the contracting muscles. Limited evidence suggests that steady-state vasodilator responses to dynamic forearm exercise are preserved or even increased in young obese humans compared with lean peers, but this topic still remains poorly understood. PURPOSE: To evaluate exercise-induced changes in hemodynamics in young obese adults compared with lean adults. METHODS: Thirteen lean (female=6; 26±1 yrs; 22.4±0.5 kg/m2) and 14 obese adults (female=7; 27±1 yrs; 32.6±0.6 kg/m2) performed 2-min of dynamic forearm exercise at 15 and 30% of maximal voluntary contraction (1-s contraction: 2-s relaxation). Ultrasonography [brachial diameter, forearm blood flow (FBF), forearm vascular conductance (FVC)], and beat-to-beat hemodynamics [mean arterial pressure (MAP), heart rate (HR), stroke index (SI), systemic vascular resistance index (SVRI), cardiac index (CI), systemic arterial compliance index (SACI)] were collected. FBF and FVC were normalized to lean forearm mass, and hemodynamics were indexed to body surface area. RESULTS: There were no group differences in any variable at baseline. Brachial artery diameter, FBF, FVC, and HR increased from baseline at 15% and 30% of MVC similarly in both groups (P<0.05). There was an interation for SVRI (P<0.05), where SVRI decreased from baseline at 15% and 30% MVC only in the lean group (P<0.05). CONCLUSION: Although young obese adults did not exhibit an impairement in exercise-induced increases in blood flow, systemic vascular resistance did not decrease with exercise in obese adults. Future studies in an older population may reveal more consistent obesity-related impairments, whereas our current cohort is young and lack comorbidities.Table: No title available.Data are mean±SE. *P<0.05, time effect. ?P<0.05, interaction. aP<0.05, different from baseline.

Blood Flow Regulation and Oxygen Uptake during High Intensity Forearm Exercise

The vascular strain is very high during heavy handgrip exercise, but the intensity and kinetics to reach peak blood flow, and peak oxygen uptake, are uncertain. PURPOSE: We included 9 young (25±2yr) healthy males to evaluate blood flow and oxygen uptake responses during continuous dynamic handgrip exercise with increasing intensity. METHODS: Blood flow was measured using Doppler-ultrasound and venous blood was drawn from a deep forearm vein to determine arteriovenous oxygen difference (a-vO2diff) during 6-minutes bouts of 60, 80 and 100% of maximal work rate (WRmax), respectively. RESULTS: Blood flow and oxygen uptake increased (p<0.05) from 60%WRmax (557±177(SD) mL[BULLET OPERATOR]min-1; 56.0±21.6 mL[BULLET OPERATOR]min-1) to 80%WRmax (679±190 mL[BULLET OPERATOR]min-1; 70.6±24.8 mL[BULLET OPERATOR]min-1), but no change was seen from 80%WRmax to 100%WRmax. Blood velocity (49.5±11.5 cm[BULLET OPERATOR]sec-1 to 58.1±11.6 cm[BULLET OPERATOR]sec-1) and brachial diameter (0.49±0.05cm to 0.50±0.06 cm) showed concomitant increases (p<0.05) with blood flow from 60% to 80%WRmax, while no differences were observed in a-vO2diff. Shear rate also increased (p<0.05) from 60% (822±196 s-1) to 80% (951±234 s-1) of WRmax. The mean response time (MRT) was slower (p<0.05) for blood flow (60%WRmax:50±22s; 80%WRmax:51±20s; 100%WRmax:51±23s) than a-vO2diff (60%WRmax:29±9s; 80%WRmax:28±5s; 100%WRmax:20±5s), but not different from oxygen uptake (60%WRmax:44±25s; 80%WRmax:43±14s; 100%WRmax:41±32s). No differences were observed in MRT for blood flow or oxygen uptake with increased exercise intensity. CONCLUSION: When approaching maximal intensity, oxygen uptake appeared to reach a critical level at ~80% of WRmax and be regulated by blood flow. This implies that high, but not maximal, exercise intensity may be an optimal stimulus for shear stress-induced small muscle mass training adaptations.

Peak Total‐[Hemoglobin + Myoglobin] During Incremental Dynamic Handgrip Exercise and Post Occlusive Hyperemia

IntroductionNear infrared spectroscopy (NIRS) has been used previously to measure changes in the total hemoglobin + myoglobin (Total‐[Hb+Mb]) signal, thought to reflect changes in microvascular hematocrit (HCT). During rest the hematocrit of the microvasculature is lower compared to the systemic hematocrit. However, during exercise microvascular hematocrit increases towards that seen in the systemic circulation. This increase in hematocrit provides an increase in the surface area available for O2 exchange. Post‐occlusive reactive hyperemia (PORH) tests have also utilized changes in NIRS signals, including Total‐[Hb+Mb], to evaluate function/dysfunction of the circulatory system. However, it is currently unclear how the peak Total‐[Hb+Mb] observed transiently following cuff release during PORH might relate to the peak Total‐[Hb+Mb] seen at task failure during incremental exercise (active hyperemia). These results could provide insight into the underlying mechanisms which control microvascular HCT.PurposeThe purpose of this investigation was to determine how the peak Total‐[Hb+Mb] achieved during incremental dynamic handgrip exercise compared to that seen during PORH.MethodsEleven men completed two testing protocols; 1) Incremental dynamic handgrip exercise to failure and 2) PORH. Exercise and PORH were performed in a supine position, with the right arm abducted to ~80° at heart level. During incremental exercise the work rate progressively increased 0.5 Watts every 30 sec until the subject could not maintain the correct contraction rate for at least 3 consecutive contractions despite verbal encouragement. The PORH test included: 1 min of baseline, 5 min occlusion of the brachial artery, and 3 min recovery after cuff release. Near‐infrared spectroscopy (NIRS) measurements were made continuously during both tests, from which the Total‐[Hb+Mb] signal was derived.ResultsThere was no difference in the mean values for peak Total‐[Hb+Mb] during the incremental test (93.0 ± 20.3 μM) and that observed during the PORH test (93.1 ± 17.7 μM) (p = 0.992). Further, peak Total‐[Hb+Mb] during PORH was significantly correlated to peak Total‐[Hb+Mb] during incremental handgrip exercise (R2 = 0.657, p = 0.002). The slope of the regression line for Peak PORH vs. Incremental was 0.930.ConclusionThese data suggest that in a given subject, similar peak values of microvascular Total‐[Hb+Mb], and thus microvascular HCT, are achieved during active and reactive hyperemia.

Influence of Muscle Fiber Recruitment on Local Vasodilation During Work‐Matched Exercise in Humans: Role for KIR Channel Activation

Under conditions of constant muscle contractile work, blood flow to active skeletal muscle is augmented with greater muscle fiber recruitment (MFR), but the mechanisms coordinating this response remain poorly understood. We tested the hypothesis that activation of inwardly‐rectifying potassium channels (KIR) underlies the augmented local vasodilation and hyperemia observed with increased MFR during work‐matched exercise in humans. We measured forearm blood flow (FBF; Doppler ultrasound) and calculated vascular conductance (FVC; quotient of FBF and mean arterial pressure) in 10 young adults (5 male, 5 female) during dynamic handgrip exercise protocols in which work was held constant but MFR was manipulated. Two bouts of rhythmic handgrip exercise (4 min each) were performed before and during local, intra‐arterial infusion of barium chloride (BaCl2) to inhibit KIR channels: 1) “High MFR,” in which participants used a pulley system to lift a load equivalent to 25% of maximal voluntary contraction (MVC) with a contraction‐to‐relaxation duty cycle of 1:7 seconds and 2) “Low MFR,” with contractions at 12.5% MVC and a 1:3 sec contraction‐to‐relaxation duty cycle. As expected, under control conditions, EMG activity of the flexor digitorum muscles was ~ 75% greater during the high vs. low MFR trial (P &lt; 0.05). In control conditions, FBF (200 ± 28 vs. 166 ± 24 ml· min−1, P &lt; 0.05) and FVC (207 ± 28 vs. 171 ± 24 ml· min−1· 100 mmHg−1, P &lt; 0.05) were greater during the high vs. low MFR trials. Inhibition of KIR channels reduced steady‐state FBF and FVC during both high and low MFR trials, and abolished the differences between the two conditions (FBF: 143 ± 23 vs. 136 ± 21 ml· min−1, P = 0.36; FVC: 140 ± 21 vs. 134 ± 21 ml· min−1· 100 mmHg−1, P = 0.32) As such, the effect of KIR channel inhibition on FBF (−28 ± 7 vs. −17 ± 6%, P = 0.059) and FVC (−32 ± 6 vs. −21 ± 6%, P &lt; 0.05) was greater in the high vs. low MFR condition. We conclude that augmenting MFR independent of contractile work elicits vasodilation via activation of KIR channels. We speculate that K+ released from skeletal muscle fibers upon repolarization may activate KIR channels and serve as a feed forward mechanism to increase muscle blood flow in proportion to the amount of muscle fibers recruited during exercise.Support or Funding InformationSupported by NIH HL119337

Static and Dynamic Handgrip Strength Endurance: Test-Retest Reproducibility

This study investigated the reliability of static and dynamic handgrip strength endurance using different protocols and indicators for the assessment of strength endurance. Forty young, healthy men and women (age, 18-22 years) performed 2 handgrip strength endurance protocols: a static protocol (sustained submaximal contraction at 50% of maximal voluntary contraction) and a dynamic one (8, 10, and 12 maximal repetitions). The participants executed each protocol twice to assess the test-retest reproducibility. Total work and total time were used as indicators of strength endurance in the static protocol; the strength recorded at each maximal repetition, the percentage change, and fatigue index were used as indicators of strength endurance in the dynamic protocol. The static protocol showed high reliability irrespective of sex and hand for total time and work. The 12-repetition dynamic protocol exhibited moderate-high reliability for repeated maximal repetitions and percentage change; the 8- and 10-repetition protocols demonstrated lower reliability irrespective of sex and hand. The fatigue index was not a reliable indicator for the assessment of dynamic handgrip endurance. Static handgrip endurance can be measured reliably using the total time and total work as indicators of strength endurance. For the evaluation of dynamic handgrip endurance, the 12-repetition protocol is recommended, using the repeated maximal repetitions and percentage change as indicators of strength endurance. Practitioners should consider the static (50% maximal voluntary contraction) and dynamic (12 repeated maximal repetitions) protocols as reliable for the assessment of handgrip strength endurance. The evaluation of static endurance in conjunction with dynamic endurance would provide more complete information about hand function.

Altered Blood Flow Response to Small Muscle Mass Exercise in Cancer Survivors Treated With Adjuvant Therapy.

BackgroundAdjuvant cancer treatments have been shown to decrease cardiac function. In addition to changes in cardiovascular risk, there are several additional functional consequences including decreases in exercise capacity and increased incidence of cancer‐related fatigue. However, the effects of adjuvant cancer treatment on peripheral vascular function during exercise in cancer survivors have not been well documented. We investigated the vascular responses to exercise in cancer survivors previously treated with adjuvant cancer therapies.Methods and ResultsPeripheral vascular responses were investigated in 11 cancer survivors previously treated with adjuvant cancer therapies (age 58±6 years, 34±30 months from diagnosis) and 9 healthy controls group matched for age, sex, and maximal voluntary contraction. A dynamic handgrip exercise test at 20% maximal voluntary contraction was performed with simultaneous measurements of forearm blood flow and mean arterial pressure. Forearm vascular conductance was calculated from forearm blood flow and mean arterial pressure. Left ventricular ejection time index (LVETi) was derived from the arterial pressure wave form. Forearm blood flow was attenuated in cancer therapies compared to control at 20% maximal voluntary contraction (189.8±53.8 vs 247.9±80.3 mL·min−1, respectively). Forearm vascular conductance was not different between groups at rest or during exercise. Mean arterial pressure response to exercise was attenuated in cancer therapies compared to controls (107.8±10.8 vs 119.2±16.2 mm Hg). LEVTi was lower in cancer therapies compared to controls.ConclusionsThese data suggest an attenuated exercise blood flow response in cancer survivors ≈34 months following adjuvant cancer therapy that may be attributed to an attenuated increase in mean arterial pressure.

Blood flow regulation and oxygen uptake during high-intensity forearm exercise.

The vascular strain is very high during heavy handgrip exercise, but the intensity and kinetics to reach peak blood flow, and peak oxygen uptake, are uncertain. We included 9 young (25 ± 2 yr) healthy males to evaluate blood flow and oxygen uptake responses during continuous dynamic handgrip exercise with increasing intensity. Blood flow was measured using Doppler-ultrasound, and venous blood was drawn from a deep forearm vein to determine arteriovenous oxygen difference (a-vO2diff) during 6-min bouts of 60, 80, and 100% of maximal work rate (WRmax), respectively. Blood flow and oxygen uptake increased (P < 0.05) from 60%WRmax [557 ± 177(SD) ml/min; 56.0 ± 21.6 ml/min] to 80%WRmax (679 ± 190 ml/min; 70.6 ± 24.8 ml/min), but no change was seen from 80%WRmax to 100%WRmax Blood velocity (49.5 ± 11.5 to 58.1 ± 11.6 cm/s) and brachial diameter (0.49 ± 0.05 to 0.50 ± 0.06 cm) showed concomitant increases (P < 0.05) with blood flow from 60% to 80%WRmax, whereas no differences were observed in a-vO2diff Shear rate also increased (P < 0.05) from 60% (822 ± 196 s-1) to 80% (951 ± 234 s-1) of WRmax The mean response time (MRT) was slower (P < 0.05) for blood flow (60%WRmax 50 ± 22 s; 80%WRmax 51 ± 20 s; 100%WRmax 51 ± 23 s) than a-vO2diff (60%WRmax 29 ± 9 s; 80%WRmax 29 ± 5 s; 100%WRmax 20 ± 5 s), but not different from oxygen uptake (60%WRmax 44 ± 25 s; 80%WRmax 43 ± 14 s; 100%WRmax 41 ± 32 s). No differences were observed in MRT for blood flow or oxygen uptake with increased exercise intensity. In conclusion, when approaching maximal intensity, oxygen uptake appeared to reach a critical level at ~80% of WRmax and be regulated by blood flow. This implies that high, but not maximal, exercise intensity may be an optimal stimulus for shear stress-induced small muscle mass training adaptations.NEW & NOTEWORTHY This study evaluated blood flow regulation and oxygen uptake during small muscle mass forearm exercise with high to maximal intensity. Despite utilizing only a fraction of cardiac output, blood flow reached a plateau at 80% of maximal work rate and regulated peak oxygen uptake. Furthermore, the results revealed that muscle contractions dictated bulk oxygen delivery and yielded three times higher peak blood flow in the relaxation phase compared with mean values.

Static and Dynamic Handgrip Endurance in Young Adults

Static and Dynamic Handgrip Endurance in Young Adults

Potentiation of the NO-cGMP pathway and blood flow responses during dynamic exercise in healthy humans.

Previous work has shown nitric oxide (NO) contributes to ~15% of the hyperemic response to dynamic exercise in healthy humans. This NO-mediated vasodilation occurs, in part, via increases in intracellular cyclic guanosine monophosphate (cGMP), which is catabolized by phosphodiesterase. We sought to examine the effect of phosphodiesterase-5 (PDE-5) inhibition on forearm blood flow (FBF) responses to dynamic handgrip exercise in healthy humans and the role of NO. We hypothesized exercise hyperemia would be augmented by sildenafil citrate (SDF, PDE-5 inhibitor). We further hypothesized any effect of SDF on exercise hyperemia would be abolished with intra-arterial infusion of the NO synthase (NOS) inhibitor L-NG-monomethyl arginine (L-NMMA). FBF (Doppler ultrasound) was assessed at rest and during 5min of dynamic forearm handgrip exercise at 15% of maximal voluntary contraction under control (saline) conditions and during 3 experimental protocols: (1) oral SDF (n=10), (2) intra-arterial L-NMMA (n=20), (3) SDF and L-NMMA (n=10). FBF responses to intra-arterial sodium nitroprusside (NTP, NO donor) were also assessed. FBF increased with exercise (p<0.01). Intra-arterial infusion of L-NMMA resulted in a reduction in exercise hyperemia (17±1 to 15±1mL/dL/min, p<0.01). Although the hyperemic response to NTP was augmented by SDF (area under the curve: 41±7 vs 61±11 AU, p<0.01), there was no effect of SDF on exercise hyperemia (p=0.33). Despite improving NTP-mediated vasodilation, oral SDF failed to augment exercise hyperemia in young, healthy adults. These observations reflect a minor contribution of NO and the cGMP pathway during exercise hyperemia in healthy young humans.

Impact of Non-Invasive Ventilation on Sympathetic Nerve Activity in Chronic Obstructive Pulmonary Disease.

Chronic obstructive pulmonary disease (COPD) is associated with elevated sympathetic nerve activity, which is probably linked to an increased cardiovascular risk, and may contribute to muscle dysfunction by heightened muscle vasoconstrictor drive. We hypothesized that resistive unloading of respiratory muscles by intermittent non-invasive ventilation (NIV) reduces sympathetic tone at rest and during subsequent handgrip exercise in patients with COPD. Muscle sympathetic nerve activity (MSNA) in the peroneal nerve, heart rate, blood pressure, CO2, and SpO2 were continuously recorded in 5 COPD patients with intermittent NIV and 11 control COPD patients without NIV. Static and dynamic handgrip exercises were performed before and after NIV. At baseline, heart rate-adjusted MSNA (bursts/100 heart beats) did not differ between groups. NIV did not significantly affect MSNA levels at rest. However, during handgrip exercises directly following NIV, MSNA was lower than before, which was significant for dynamic handgrip (67.00±3.70 vs. 62.13±4.50 bursts/100 heart beats; p=0.035 in paired t test). In contrast, MSNA (non-significantly) increased in the control group during repeated dynamic or static handgrip. During dynamic handgrip, tCO2 was lower after NIV than before (change by -5.04±0.68mmHg vs. -0.53±0.64 in the control group; p=0.021), while systolic and diastolic blood pressure did not change significantly. NIV reduces sympathetic activation during subsequent dynamic handgrip exercise and thereby may elicit positive effects on the cardiovascular system as well as on muscle function in patients with COPD.

W′ expenditure and reconstitution during severe intensity constant power exercise: mechanistic insight into the determinants of W′

The sustainable duration of severe intensity exercise is well‐predicted by critical power (CP) and the curvature constant (W′). The development of the W′BAL model allows for the pattern of W′ expenditure and reconstitution to be characterized and this model has been applied to intermittent exercise protocols. The purpose of this investigation was to assess the influence of relaxation phase duration and exercise intensity on W′ reconstitution during dynamic constant power severe intensity exercise. Six men (24.6 ± 0.9 years, height: 173.5 ± 1.9 cm, body mass: 78.9 ± 5.6 kg) performed severe intensity dynamic handgrip exercise to task failure using 50% and 20% duty cycles. The W′BAL model was fit to each exercise test and the time constant for W′ reconstitution (τ W′) was determined. The τ W′ was significantly longer for the 50% duty cycle (1640 ± 262 sec) than the 20% duty cycle (863 ± 84 sec, P = 0.02). Additionally, the relationship between τ W′ and CP was well described as an exponential decay (r 2 = 0.90, P < 0.0001). In conclusion, the W′BAL model is able to characterize the expenditure and reconstitution of W′ across the contraction–relaxation cycles comprising severe intensity constant power handgrip exercise. Moreover, the reconstitution of W′ during constant power severe intensity exercise is influenced by the relative exercise intensity, the duration of relaxation between contractions, and CP.

Endothelial function in prehypertensive during dynamic handgrip exercise

Endothelial function in prehypertensive during dynamic handgrip exercise

Measurement of Nitric Oxide with EPR in Whole Blood during Peak Hand Grip Exercise in Women with Metabolic Syndrome

The contribution of bioavailable Nitric Oxide to the change in vascular function during exercise hyperemia is primarily concluded through the lack of functional changes in the presence of eNOS inhibitors. The aim of this study is to utilize EPR techniques to measure the changes in NO production during peak hand grip exercise to identify mechanistic differences of vascular function in women with Metabolic Syndrome compared to healthy controls.MethodsIn this study, 13 participants (5 MetSyn and 8 Controls) performed the procedure of graded handgrip exercise on a dynamic handgrip device while brachial blood flow was continuously measured with Doppler ultrasound and B‐mode (GE Vivid E with 6MHz linear probe). Following a brief rest, individuals were asked to perform handgrip exercise whereby the workload progressively increased in a ramp fashion (0.5 kg·min−1) until the required contraction rate (30 cpm) could no longer be maintained. At rest and immediately after halting exercise at task failure for individual peak resistance, whole blood was drawn into a prepared vaccutainer in a 1:1 venous blood to the metal chelator, defferoxamine (DF), in diethyldithiocarbamate (DETC) Krebs buffer. The samples were immediately flash frozen in liquid nitrogen and stored at −80 degrees Celsius. All pre and peak NO samples were measured and compared with known NO samples using an X‐band electron paramagnetic resonance spectrometer (Bruker Biospin, Karlsruhe, Germany). Whole blood with known concentrations of NO2 (1–10mM) and Na2S2O4 (20 mM) served as a reference.ResultsWhole blood NO increased significantly from rest to peak exercise in both groups (p=0.047) in addition to brachial conductance (p=0.0001). There was no significant difference in the rise in NO during peak exercise between the MetSyn and Control groups (p=0.67) however there is a significant difference in brachial conductance starting, peak and delta between the groups (p=0.021, 0.028, and 0.019).ConclusionThe whole blood Iron Chelated EPR technique is capable of detecting the degree of change in NO potentially contributing exercise hyperemia in different groups and potentially at variable grades of exercise. Although there is a significant difference in the vascular conductance between the groups, with the number of participants included in this study, there was no difference indicated between the groups for NO at rest and peak exercise.Support or Funding InformationResearch reported in this publication was supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P20GM103451.

Individual Differences in Components of the Pressor Responses to Isometric and Dynamic Handgrip Exercise in Humans

The aim of this study was to test the hypotheses that, in humans, cardiac output (CO) and total peripheral vascular resistance (TPR) responses to dynamic handgrip exercise vary among individuals as demonstrated recently with isometric handgrip exercise, and that the responses of the components mediating the pressor response have a similarity between those exercises in the same individuals. We studied 30 healthy male and female volunteers with a mean age of 25 ± 0.5 yr, body weight of 64 ± 2.4 kg, and height of 169 ± 1.5 cm (means ± SE). The subjects assumed a supine position and performed isometric and dynamic (30 contractions/min) handgrip exercise at 50% of maximal voluntary contraction until fatigue separately (84 ± 3 s and 178 ± 14 s, respectively). We assessed the magnitude of the variance in the individual changes in mean arterial pressure (MAP), CO and TPR at 20%, 40%, 60%, 80% and 100% of fatigue using inter individual coefficient of variation (CV). Although CVs for changes in CO and TPR between the rest and the exercise periods were not much different from the CV for change in MAP at 20% of fatigue, the CVs for changes in CO and TPR were 2‐ to 3‐fold greater than the CV for change in MAP at ≥40% of fatigue in both trials. Thus the components of the pressor responses to isometric as well as dynamic handgrip exercise varied widely among subjects at ≥40% of fatigue. In addition, the CO and TPR responses during dynamic handgrip exercise correlated positively with the corresponding responses during isometric handgrip exercise from 20% to 100% of fatigue (CO: r = 0.675–0.755, P &lt; 0.01; TPR: r = 0.566–0.788, P &lt; 0.01). Our findings demonstrate that the CO and TPR responses during moderate to exhaustive handgrip exercise (≥40% of fatigue) vary considerably among individuals compared to the pressor response irrespective of the exercise modality (isometric or dynamic). They also suggest that the CO and TPR responses to handgrip exercise is similar between the modalities in the same individuals throughout the course of exercise.Support or Funding InformationThis study was supported by the grants from Japan Society for the Promotion of Science.

Ischemic preconditioning reduces hemodynamic response during metaboreflex activation.

Ischemic preconditioning (IP) has been shown to improve exercise performance and to delay fatigue. However, the precise mechanisms through which IP operates remain elusive. It has been hypothesized that IP lowers the sensation of fatigue by reducing the discharge of group III and IV nerve endings, which also regulate hemodynamics during the metaboreflex. We hypothesized that IP reduces the blood pressure response during the metaboreflex. Fourteen healthy males (age between 25 and 48 yr) participated in this study. They underwent the following randomly assigned protocol: postexercise muscle ischemia (PEMI) test, during which the metaboreflex was elicited after dynamic handgrip; control exercise recovery session (CER) test; and PEMI after IP (IP-PEMI) test. IP was obtained by occluding forearm circulation for three cycles of 5 min spaced by 5 min of reperfusion. Hemodynamics were evaluated by echocardiography and impedance cardiography. The main results were that after IP the mean arterial pressure response was reduced compared with the PEMI test (means ± SD +3.37 ± 6.41 vs. +9.16 ± 7.09 mmHg, respectively). This was the consequence of an impaired venous return that impaired the stroke volume during the IP-PEMI more than during the PEMI test (-1.43 ± 15.35 vs. +10.28 ± 10.479 ml, respectively). It was concluded that during the metaboreflex, IP affects hemodynamics mainly because it impairs the capacity to augment venous return and to recruit the cardiac preload reserve. It was hypothesized that this is the consequence of an increased nitric oxide production, which reduces the possibility to constrict venous capacity vessels.

Sympathetic Activation is Associated with Exercise Limitation in COPD

ABSTRACTExercise intolerance, skeletal muscle dysfunction, and reduced daily activity are central in COPD patients and closely related to quality of life and prognosis. Studies assessing muscle exercise have revealed an increase in sympathetic outflow as a link to muscle hypoperfusion and exercise limitation. Our primary hypothesis was that muscle sympathetic nerve activity (MSNA) correlates with exercise limitation in COPD.MSNA was evaluated at rest and during dynamic or static handgrip exercise. Additionally, we assessed heart rate, blood pressure, CO2 tension, oxygen saturation (SpO2), and breathing frequency. Ergospirometry was performed to evaluate exercise capacity.We assessed MSNA of 14 COPD patients and 8 controls. In patients, MSNA was negatively correlated with peak oxygen uptake (VO2% pred) (r = −0.597; p = 0.040). During dynamic or static handgrip exercise, patients exhibited a significant increase in MSNA, which was not observed in the control group. The increase in MSNA during dynamic handgrip was highly negatively correlated with peak exercise capacity in Watts (w) and peak oxygen uptake (VO2/kg) (r = −0.853; p = 0.002 and r = −0.881; p = 0.002, respectively).Our study reveals an association between increased MSNA and limited exercise capacity in patients with COPD. Furthermore, we found an increased sympathetic response to moderate physical exercise (handgrip), which may contribute to exercise intolerance in COPD.

Effects of disturbed blood flow during exercise on endothelial function: a time course analysis.

This study aimed to examine the time course of endothelial function after a single handgrip exercise session combined with blood flow restriction in healthy young men. Nine participants (28±5.8 years) completed a single session of bilateral dynamic handgrip exercise (20 min with 60% of the maximum voluntary contraction). To induce blood flow restriction, a cuff was placed 2 cm below the antecubital fossa in the experimental arm. This cuff was inflated to 80 mmHg before initiation of exercise and maintained through the duration of the protocol. The experimental arm and control arm were randomly selected for all subjects. Brachial artery flow-mediated dilation (FMD) and blood flow velocity profiles were assessed using Doppler ultrasonography before initiation of the exercise, and at 15 and 60 min after its cessation. Blood flow velocity profiles were also assessed during exercise. There was a significant increase in FMD 15 min after exercise in the control arm compared with before exercise (64.09%±16.59%, P=0.001), but there was no change in the experimental arm (-12.48%±12.64%, P=0.252). FMD values at 15 min post-exercise were significantly higher for the control arm in comparison to the experimental arm (P=0.004). FMD returned to near baseline values at 60 min after exercise, with no significant difference between arms (P=0.424). A single handgrip exercise bout provoked an acute increase in FMD 15 min after exercise, returning to near baseline values at 60 min. This response was blunted by the addition of an inflated pneumatic cuff to the exercising arm.

Influence of prior anterograde shear rate exposure on exercise-induced brachial artery dilation.

Shear rate can elicit substantial adaptations to vascular endothelial function. Recent studies indicate that prior exposure to anterograde flow and shear increases endothelium-dependent flow-mediated dilation at rest and that anterograde shear can create an anti-atherosclerotic and provasodilatory state. The primary aim of the present study was therefore to determine the effects of prior exposure to anterograde shear on exercise-induced brachial artery dilation, total forearm blood flow (FBF), and vascular conductance (FVC) during dynamic handgrip exercise. Eight men completed a constant-load exercise test corresponding to 10% maximal voluntary contraction, prior to (baseline) and following a 40 min shear rate intervention (post-SRI) achieved via unilateral forearm heating, which has previously been shown to increase anterograde shear rate in the brachial artery. During the SRI, anterograde shear rate increased 60.9 ± 29.2 sec−1 above baseline (P < 0.05). Post-SRI, the exercise-induced brachial artery vasodilation was significantly increased compared to baseline (4.1 ± 0.7 vs. 4.3 ± 0.6 mm, P < 0.05). Post-SRI FBF mean response time (33.2 ± 16.0 vs. 23.0 ± 11.8 sec, P < 0.05) and FVC mean response time (31.1 ± 12.8 20.2 ± 10.7 sec, P < 0.05) at exercise onset were accelerated compared to baseline. These findings demonstrate that prior exposure to anterograde shear rate increases the vascular responses to exercise and supports the possible beneficial effects of anterograde shear rate in vivo.

Racial Differences In Hrv In Response To An Acute Bout Of Forearm Exercise

Cardiovascular disease, more prevalent in older individuals and in African Americans (AA), may be due in part to differences in autonomic control. Heart rate variability (HRV), a non-invasive measure of cardiac autonomic function, has demonstrated conflicting results comparing parasympathetic function in AA. A sympatho-excitatory task, like handgrip exercise, may help determine if racial differences exist in relation to autonomic control. PURPOSE: Using HRV to o elucidate racial differences in cardiac autonomic function, between AA and Caucasians (CA) at rest and during dynamic handgrip exercise. METHODS: Healthy older AA (n=13, 59yrs) and CA (n=13, 60yrs) adults performed dynamic handgrip exercise (20 contractions/min) for 3 min at 10% and 20% maximum voluntary contraction (MVC). HRV was measured at rest and during exercise. HRV indices included time (root mean square of successive differences, RMSSD) and frequency domain parameters (low frequency (LF), high frequency (HF) and the LF/HF ratio. RESULTS: CA exhibited a higher LF/HF ratio compared to AA during all conditions (p<0.05), see table. RMSSD, LF, and HF decreased while HR all increased with exercise (p<0.05), but there were no racial differences. CONCLUSIONS: AA demonstrated lower LF/HF ratio at rest and during exercise compared to CA. This difference appears to be driven by higher HF in the AA at all time points, suggesting greater parasympathetic dominance.

Effects of Chemotherapy and Radiation Exposure on Brachial Artery Blood Flow during Dynamic Handgrip Exercise

Chemotherapy and radiation cancer treatments have been shown to alter peripheral cardiovascular function. Therefore, the purpose of this study was to investigate if the vascular responses to dynamic handgrip exercise are blunted in individuals who have undergone chemotherapy and/or radiation treatment. To date, 1 cancer survivor (CS) and 1 healthy control (HC) have completed two dynamic handgrip exercise protocols at relative (10 and 20% maximal voluntary contraction (MVC)) and absolute (3 and 9 kg) workloads. Simultaneous measurements of forearm blood flow (FBF; Doppler Ultrasound), and mean arterial pressure (MAP) were taken during each of the workloads. Forearm vascular conductance (FVC) was calculated from MAP and FBF. Plasma concentrations of endothelial microparticles (EMPs) which are suggestive of apoptotic and activated endothelial cells (CD31+/CD42b‐ and CD62E+ EMPs, respectively) were isolated from venous blood samples. Preliminary results: FBF was decreased in CS compared to HC at: 10% MVC (111.72 vs. 228.17 ml min‐1) and 20% MVC (148.60 vs. 362.53 ml min‐1). FVC was reduced in CS when compared to HC at: 10% MVC (107.65 vs. 205.32 ml min‐1 100 mmHg‐1) and 20% MVC (135.35 vs. 287.64 ml min‐1 100 mmHg‐1). During absolute workloads FBF and FVC of the CS compared to HC was similar at 3 kg (143.91 vs. 135.26 ml min‐1 and 162.33 vs. 124.42 ml min‐1 100 mmHg‐1, respectively), but less at 9 kg (156.11 vs. 307.42 ml min‐1 and 155.24 vs. 263.54 ml min‐1 100 mmHg‐1, respectively). Due to time constraints plasma EMP concentrations are unavailable at this time. In conclusion, chemotherapy and radiation treatment in cancer survivors results in alterations to exercise blood flow regulation during dynamic exercise.